Device and method for monitoring an access to a patient

Abstract

The present invention relates to a device and a method for monitoring a patient access, particularly for monitoring the venous vascular access in extracorporeal blood treatment where blood is withdrawn from the patient via a flexible arterial line which has an arterial needle or cannula, and provided to the patient via a flexible venous line which has a venous needle or cannula. The needle or cannula of the present invention is so designed that, due to the liquid flowing through the needle or cannula, air is drawn in if the needle or cannula is out of the vascular access, whereby sound is generated. A vascular access which is not in proper order is detected with great certainty and reliability by monitoring the surrounding environment for the occurrence of sound, particularly for the occurrence of the solid-borne sound which propagates along the flexible venous line of the extracorporeal blood circuit.

The invention claimed is: 
     
       1. A device for monitoring an access to a patient of an apparatus by which a liquid is provided to the patient via a needle or cannula comprising:
 a needle or cannula comprising a narrowed cross-section comprising a constriction for flow to generate a pressure below atmospheric due to the liquid flowing through the needle or cannula, wherein cross-sections on both sides of the narrowed cross-section are wider than the narrowed cross-section, said narrowed cross-section having an opening, the opening entirely within a region of the narrowed cross-section, the opening comprising a through-hole or a milled aperture within the constriction of the needle or cannula, and the needle or cannula being configured such that, if the needle or cannula is out of the access then, due to the liquid flowing through the needle or cannula, the needle or cannula draws in air through the opening, thereby causing a sound to be generated; and 
 an analyzing unit for sensing the generated sound, said analyzing unit being configured such that, when the generated sound is sensed, it is determined that the patient access is not in proper order. 
 
     
     
       2. The device of  claim 1 , wherein the analyzing unit comprises:
 a sound converter for converting a sound signal into an electrical signal; or 
 a laser for scanning a surface or an acceleration sensor which generate an electrical signal. 
 
     
     
       3. The device of  claim 2 , wherein the sound converter comprises a converter of solid-borne sound for converting solid-borne sound into electrical signals. 
     
     
       4. The device of  claim 3 , wherein the device is for monitoring the venous vascular access in the case of an extracorporeal blood treatment where blood is withdrawn from the patient via a flexible arterial line which has an arterial needle or cannula and blood is provided to the patient via a flexible venous line which has a venous needle or cannula, and
 wherein the converter of solid-borne sound is arranged on the flexible venous line to sense solid-borne sound which propagates along the flexible venous line. 
 
     
     
       5. The device of  claim 2 , wherein the analyzing unit comprises:
 a comparison unit for comparing an amplitude of the electrical signal with an amplitude of a preset reference signal, the analyzing unit being configured to determine that a patient access is not in proper order if the amplitude of the electrical signal is higher than the amplitude of the preset reference signal. 
 
     
     
       6. The device of  claim 2 , wherein the analyzing unit comprises:
 a comparison unit for comparing the electrical signal with a characteristic signal pattern, the analyzing unit being configured to determine that a patient access is not in proper order if the characteristic signal pattern is detected in the electrical signal. 
 
     
     
       7. The device of  claim 1 , further comprising:
 an alarm unit configured to give an audio and/or visual alarm if it is detected that a patient access is not in proper order. 
 
     
     
       8. A blood treatment apparatus having an extracorporeal blood circuit comprising:
 a flexible arterial line having an arterial needle or cannula, 
 a flexible venous line having a venous needle or cannula, and 
 the device for monitoring the access to a patient of  claim 1 . 
 
     
     
       9. The device of  claim 1 , for monitoring the venous vascular access in the case of an extracorporeal blood treatment where blood is withdrawn from the patient via a flexible arterial line which has an arterial needle or cannula and blood is provided to the patient via a flexible venous line which has a venous needle or cannula, further comprising:
 a control unit configured to generate a signal in a control system of a blood treatment apparatus to interrupt the treatment of the blood. 
 
     
     
       10. The device of  claim 4 , wherein the analyzing unit comprises:
 a comparison unit for comparing an amplitude of the electrical signal with an amplitude of a preset reference signal, the analyzing unit being configured to determine that a patient access is not in proper order if the amplitude of the electrical signal is higher than the amplitude of the preset reference signal. 
 
     
     
       11. The device of  claim 4 , wherein the analyzing unit comprises:
 a comparison unit for comparing the electrical signal with a characteristic signal pattern, the analyzing unit being configured to determine that a patient access is not in proper order if the characteristic signal pattern is detected in the electrical signal. 
 
     
     
       12. The device of  claim 7 , for monitoring the venous vascular access in the case of an extracorporeal blood treatment where blood is withdrawn from the patient via a flexible arterial line which has an arterial needle or cannula and blood is provided to the patient via a flexible venous line which has a venous needle or cannula, further comprising:
 a control unit configured to generate a signal in a control system of a blood treatment apparatus to interrupt the treatment of the blood. 
 
     
     
       13. The device of  claim 1 , wherein the opening is in a surface of the needle or cannula which is not parallel to the narrowed cross-section.